The technical field of this invention is the implantation of ions into targets, such as semiconductor wafers, and, in particular, systems and techniques for achieving highly uniform implantation doses for the formation of buried layer devices and the like.
Ion implantation techniques are particularly useful in forming a class of buried layer devices known as silicon-on-insulator (SOI) devices. In these devices, a buried insulation layer is formed beneath a thin surface silicon film. These devices have a number of potential advantages over conventional silicon devices (e.g., higher speed performance, higher temperature performance and increased radiation hardness).
In one known technique, known by the acronym SIMOX, a very thin (1,000 Angstroms-3,000 Angstroms) layer of a monocrystalline silicon substrate is separated from the bulk of the substrate by implanting oxygen ions (e.g., with an implant dose of about 1.0.times.10.sup.18 to 3.0.times.10.sup.18 oxygen ions per square centimeter) into the substrate to form a buried dielectric layer (having a typical thickness ranging from about 1,000 Angstroms to 5,000 Angstroms). This technique of "separation by implanted oxygen" (SIMOX), provides a heterostructure in which a buried silicon dioxide layer serves as a highly effective insulator for surface layer electronic devices.
Because of the high dosages required to produce buried silicon dioxide layers, conventional SIMOX techniques are often very time-consuming. The implantation dose that can be delivered to a substrate over any given period of time is largely a function of the current density and power of the implantation ion beam. In practice, there is a limit on the power which can be achieved by conventional ion implanters; typically, when the implantation current rises above about 75 milliamps, the beam becomes very unwieldy and either thermal damage or erratic implantation profiles ensue. For these reasons, lower current densities are often employed in SIMOX fabrication techniques and, as a result, the implantation process can take as long as 24 hours.
There exist a need for better techniques for ion implantation, particularly, techniques which would reduce the time necessary to implant buried layers in target substrates and/or improve the uniformity of the implants.